It has become well accepted, if not universally accepted, that to ensure a proper seating of a hip stem implant and to reduce failure rates at the bone/prosthesis junction the prosthesis when seated should withstand a predetermined amount of torque without significant movement relative to the femur. Typically, this type of testing is accomplished by connecting a torque wrench to the rasp handle or implant. If visual movement between the rasp or prosthesis and femur is not observed by the surgeon when torque of approximately 180 inch pounds is applied, it is believed that the medullary canal of the femur is properly prepared for accommodating the appropriate size of hip stem implant. A more thorough explanation of the necessity of torsional testing of a rasp and hip stem implant may be had by reference to U.S. Pat. No. 4,922,898 issued to Dunn and incorporated herein by reference.
A prosthetic hip stem implant with a torque adapter designed to connect a torque wrench to the implant without marring the finish of the implant is illustrated and described in U.S. patent application Ser. No. 603,338 filed on Nov. 5, 1990 and incorporated herein by reference.
The torque adapters and method of the above identified patent and application for patent, rely on the surgeon to closely monitor the bone/prosthesis junction to determine if movement occurs while torque force is applied to the implant.